As lawmakers race to negotiate a deal to avoid the fiscal cliff, some experts say one tax increase should be on the table: a gas tax hike.

Currently at 18.4 cents a gallon, the federal gas tax is used primarily to build and repair roads, bridges and other transportation infrastructure. The tax raises about $32 billion a year.

But that's not enough. The government hands out about $50 billion a year to states and towns to help with road costs. The difference comes out of general funds or has to be borrowed. Meanwhile, the gas tax hasn't been raised since 1993.